SUMMARY OF THE PRESENT INVENTION
This invention relates to an apparatus for separating aggregates from an asphalt-aggregate mixture. Such separation is useful as part of a procedure for testing the mixture for asphalt content and particle size distribution in the mixture. Such testing is performed as a quality control function in the process of formulating and building asphalt pavement.
Conventional asphalt pavement commonly comprises a prepared subgrade (or foundation soil), a base layer on the subgrade, and asphalt surface layer laid on the base layer. The base layer can comprise an asphalt-aggregate mixture, or compacted aggregates (without the asphalt); typically the base layer is at least three inches thick when asphalt is used therein, and at least six inches thick when no asphalt is used. The aggregates in the base layer typically will have maximum diameters in the range of from one-half inch to about one and one-half inch.
The asphalt surface layer will typically have a thickness of about one inch. The aggregates (rocks) in the surface layer will have somewhat smaller maximum diameters, from about three-quarters inch to about one-quarter inch.
The asphalt and aggregates are mixed together until the aggregates are individually coated with the asphalt. The mixing operation is carried out with both the aggregates and asphalt preheated, in order to dry the aggregates and thereby prevent moisture from existing within the final mix. The mixing operation is commonly termed a hot mix batching operation.
The hot mixture is transported to the area where the pavement is to be laid, and spread in a partially compacted layer to a reasonably uniform surface condition. While the mixture is still hot a heavy roller is run over the surface a number of times to compact the mixture and form a smooth surface. The same procedure is used for the asphalt-aggregate base layer, and for the asphalt aggregate surface layer.
The proportion of aggregate to asphalt is kept within limits, based on experience and job specifications. Also, by controlling the aggregate particle size distribution and the asphalt content, the percentage of voids in the mixture is kept within limits. Typically, the acceptable void percentage is in the range of from three to four percent. When the void percentage is higher than six to eight percent, the pavement may deteriorate prematurely.
In order to verify the properties of the asphalt-aggregate mixture, test samples are taken at various times in the process, e.g., after a batch mixing operation at the mixing facility, or from a section of pavement at the pavement site. Testing of the asphalt-aggregate sample involves extracting the asphalt from the aggregate.
The testing operation can take various different forms and practices. However, in one particular procedure the weight of the test sample is recorded, after which the sample is placed in a centrifuge to extract the asphalt from the aggregate. Organic solvent will be added to the centrifuge to dissolve the asphalt, such that the dissolved asphalt (in liquid form) can be drained out of the centrifuge, through a filter, leaving the bare aggregate in the centrifuge. Warm water is then added to the aggregate to remove the solvent from the aggregate. The water removes the solvent and it is drained out of the centrifuge through a filter.
The bare aggregate is removed from the bowl and dried in an oven to remove water from the aggregate surface. The aggregate is then weighed.
The asphalt-extraction process, in conjunction with the weighing operations, enables the technician to determine the asphalt content of the sample. The size range of the aggregates can be determined by passing the bare aggregates through a range of different square mesh size sieves.
The present invention is concerned with an economical and efficient apparatus for extracting asphalt from an aggregate-asphalt mixture, as part of the aforementioned testing process.
The apparatus comprises a timer-controlled valve system for delivering predetermined quantities of organic solvent, soap and water to the centrifuge such that the aggregate-asphalt mixture in the centrifuge is subjected automatically to a series of cleaning (asphalt extraction) activities. The apparatus times the activities and the quantities of solvent, soap and water, so that the process becomes standardized and automatic; the human element, and the possibility of human error and miscalculations, is eliminated, so that the asphalt extraction process is quicker, more efficient and reliable.
In preferred practice of the invention, the timing and control functions are accomplished with a programmable controller, e.g. TEXAS INSTRUMENTS model 315 Central Processing Unit, or a corresponding processor manufactured by the SIEMENS COMPANY.
When a programmable controller is used for the timing and controlling function, the cycle can be altered or changed to meet different conditions, e.g. different sample sizes, different solvents, and different asphalt qualities and quantities.
The principal aim of the invention is to carry out the asphalt extraction procedure more efficiently and quickly, with reduced expenditures for solvents and soaps, and with minimum human involvement in the process. Further features of the invention will be apparent from the attached drawings and description of a preferred embodiment of the invention.
In summary, and in accordance with the above-discussion, the foregoing objectives are achieved in the following embodiments.
1. Apparatus for extracting asphalt from an asphalt-aggregate mixture, comprising:
a centrifuge that includes a rotary bowl, an electric motor for rotating said bowl around a vertical axis, and a drain for the flow of liquid out of said centrifuge; PA1 an organic solvent supply source having a first electrical control means; PA1 a warm water supply source having a second electrical control means; PA1 a liquid soap supply source having a third electrical control means; PA1 means for delivering solvent from said solvent source to said bowl; PA1 means for delivering water and scrap from said water and soap sources to said bowl; and PA1 a timer means having separate plural outputs connected to said motor, first control means, second control means, and third control means; whereby the solvent, water and soap can be cyclically delivered to the rotatable bowl, and dissolved asphalt can be drained out of the bowl on an automatic timed cycle. PA1 means for swinging said liquid conduit in a horizontal arc between an inactive position offset laterally from said centrifuge, and an active position overlying the centrifuge; and PA1 said discharge spout being operable to direct solvent into said bowl when said liquid conduit is in its active position. PA1 means for swinging said liquid conduit in a horizontal arc between an inactive position offset laterally from said centrifuge, and an active position overlying the centrifuge; and PA1 said discharge spout being operable to direct water and soap downwardly into said bowl when said liquid conduit is in its active position. PA1 means pivotably supporting said arm for swinging motion in a horizontal plane between a standby position offset from the centrifuge and an operating position overlying the centrifuge; PA1 said solvent delivery means comprising a first liquid conduit extending along said arm, said conduit having a liquid inlet near said pivot support means and a downwardly-directed discharge spout remote from said pivot support means; PA1 said water and soap delivery means comprising a second liquid conduit extending along said arm, said second conduit having a liquid inlet near said pivot support means and a downwardly-directed discharge spout remote from said pivot support means; and PA1 each said conduit being operable to discharge liquid downwardly into said bowl when said art is in its operating position.
2. The apparatus, as described in paragraph 1, wherein said timer means is a programmable controller.
3. The apparatus, as described in paragraph 1, wherein said timer means provides at least one solvent soak activity, at least one soapy wash activity, and at least one clean water rinse activity for the asphalt-aggregate mixture in said bowl.
4. The apparatus, as described in paragraph 3, wherein said timer means provides a liquid drain action after each solvent soak activity, soapy wash activity, and water rinse activity.
5. The apparatus, as described in paragraph 1, wherein said solvent delivery means comprises a liquid conduit having a downwardly-directed discharge spout;
6. The apparatus, as described in paragraph 1, wherein said water and soap delivery means comprises a liquid conduit having a downwardly-directed discharge spout;
7. The apparatus, as described in paragraph 1, and further comprising a horizontal arm;
8. The apparatus, as described in paragraph 7, and further comprising a first flexible hose connected to the inlet on said first conduit, and a second flexible hose connected to the inlet on said second conduit, whereby said hoses are enabled to deliver liquids to the respective conduits without preventing horizontal swinging motion of said arm.